The
Compressor transports the refrigerant
at the required pressure through the air
conditioning system. The refrigerant is
a low pressure gas as it enters the
Compressor from the Evaporator. The
Compressor increases the
refrigerant pressure and also
its temperature so it becomes a high
pressure gas which, in turn, helps the
refrigerant condense more rapidly in the
next component, which is the Condenser.
The Compressor is mounted on the engine
and is driven by a belt from
the engine's crankshaft pulley. The
most common reasons for failure are lack
of oil, pulley bearing wear,
electromagnetic coil burn-out and lack
of regular servicing.

CONDENSER:

The
Condenser works in the opposite way to
the Evaporator. The refrigerant gives
up its heat generated by the Compressor
by passing cold air across its fins and
tubes by ram air or by an extra fan.
The end result of this change is that
the refrigerant is now a high pressure
liquid and is forced out to the Receiver
Drier through the liquid line. Because
the Condenser is usually located at the
front of the vehicle it can become
damaged by debris or corroded by
materials from the road. It can also
fail because of weak spots in its
construction and also lack of regular
servicing.

FILTER
DRIER:

Depending
on the type of air conditioning system
fitted, this item can be called a
Receiver Drier or an Accumulator.
(The Accumulator is fitted on the low
pressure gas line of an air conditioning
system between the Compressor and the
Evaporator and is used in conjunction
with an orifice tube). The Receiver
Drier is fitted on the high pressure
liquid line of an air conditioning
system between the Condenser and
Expansion Device. The Receiver Drier
has two parts to it, the receiver and,
of course, the drier. The receiver
section holds the right amount of
refrigerant required by the system to
ensure correct operation and to supply a
steady flow of liquid refrigerant to the
Expansion Device. The drier section is
responsible for removing moisture from
the air conditioning system by means of
a bag of desiccant which absorbs small
quantities of moisture. This is a very
important part of the air conditioning
system and should be changed at least
every two years or when the system is
repaired. The most common reasons for
failure is corrosion and desiccant
deterioration which leads to severe
system failure.

EXPANSION
DEVICE:

The
Expansion Device comes in many forms.
It can be a brass internally or
externally equalised valve, a block type
valve or an orifice tube (the latter
being part of an Accumulator type air
conditioning system). Expansion
Device's have an inlet and an outlet
which separates the high side of the
system from the low side. A small
restriction in the valve allows only a
small amount of refrigerant to pass
through it into the Evaporator, the
amount of refrigerant passing through
the valve depends on the Evaporator
temperature. The most common reasons
for failure are contamination, moisture
and lack of regular servicing.

EVAPORATOR:

As soon as
the liquid pressure drops, the
refrigerant begins to boil (R134A
refrigerant boils at approximately -26
degrees centigrade). As it continues to
boil the Evaporator absorbs the heat
passing over its tubes and fins and as a
result the air is cooled. Remember
that heat is being removed from the warm
air and cold air is not being created.
The compressor, on its suction side,
removes the low pressure vapour from the
Evaporator and the cycle starts all
over again. The most common reasons for
failure are corrosion, weak spots in
construction and lack of regular
servicing.

THE COOLING PROCESS EXPLAINED

Wet your finger and wave it in the air.
What you are feeling is a refrigeration
effect. When a liquid turns to a vapor
it absorbs heat. In this case it is
sucking the heat out of your finger.

The opposite is also true. If that vapor
then loses that heat, it will turn back
into a liquid.

In a refrigeration system, we force a
liquid to become a vapor in the
evaporator, thus absorbing heat from the
refrigerated space.

We then use a compressor to pump that
vapor to the condenser.

In the condenser we force that vapor to
reject the heat and thus turn back into
a liquid so that we can re-use it.

We then meter the liquid back into the
evaporator to complete the loop and do
it all over again and again and again.

How do we force a liquid to become a
vapor?... or a vapor to become a liquid?
By manipulating its boiling point.

The boiling point is the temperature at
which the liquid turns to vapor when
heat is added. It is also the
temperature at which a vapor turns to
liquid when heat is removed.

Boiling point = saturation temp =
evaporating temp = condensing temp

When we think of the boiling point of a
liquid it is the boiling point at zero
psi pressure. If we increase its
pressure we raise its boiling point. If
we decrease its pressure we lower its
boiling point.

In the evaporator we force liquid to
become a vapor by lowering its pressure
until its boiling point/evaporating
temperature is lower than the air it is
trying to cool.

In the condenser we force the vapor to
become a liquid by raising its pressure
until its boiling point/condensing
temperature is higher than the air it is
trying to heat.

Different substances have different
boiling points at different pressures.

We can tell what the boiling
point/saturation temp/evaporating
temp/condensing temp is at various
pressures for common refrigerants by
checking a pressure/temperature chart.